In hydraulic mounts such as those used in motor vehicle engine mounting systems, the mount normally comprises a pair of mounting members, an elastomeric body, an elastomeric diaphragm, a decoupler and a damping orifice. The elastomeric body connects the mounting members and the diaphragm which is connected to only one of the mounting members cooperates with the elastomeric body to define a closed cavity. The partition divides the cavity into a chamber that is enclosed by one side of the partition and the elastomeric body and another chamber that is enclosed by the other side of the partition and the diaphragm. A liquid fills the chambers and the damping orifice connects these chambers to provide a damping effect by throttling the flow passing therethrough.
In such hydraulic engine mounts, it is desirable to eliminate damping at small engine displacements such as caused by high speed road transmitted vibrations. This is normally accomplished by the decoupler which is typically mounted for unrestrained reciprocal movement within prescribed limits on the partition and is open on opposite sides thereof to the chambers thereby to effect limited cyclic volume change in the chambers so as to then not force flow between the chambers through the damping orifice. In addition, it has also been the practice to allow some restrained movement of the entire partition to supplement the decoupling effect provided by the decoupler. For example, see U.S. Pat. Nos. 4,588,173 and 4,611,795 assigned to the assignee of the present invention which disclose the various details of such prior hydraulic engine mount designs.